Generally, a brush cutter has an engine driven by using gasoline as fuel, at the rear of a handle pipe. And, rotary blades at the front of the handle pipe driven by the engine through a centrifugal clutch mechanism. In such brush cutter, the user is allowed to control the output (rotation) of the engine by operating a throttle lever with their finger while holding the grip of the handle pipe, as necessary.
For example, JP-4211959-B proposes a throttle adjustment device (lever device) for a brush cutter, as shown in FIG. 13. In the throttle adjustment device, a throttle adjustment wire 53 (Bowden wire) is extended from an engine (not shown), and a drum 54 is provided at an end of the throttle adjustment wire 53. The throttle adjustment device includes a throttle lever 57 having a drum holding portion 55 for holding the drum 54 and an engagement wall 59, and a sub lever 58 having a regulating member 60 to be faced to the engagement wall 59. The throttle lever 57 and the sub lever 58 are rotatably disposed in a case 52 fixed to a handle pipe 51. The rotation range of the throttle lever 57 is adjusted by the sub lever 58 through a contact between the regulating member 60 and the engagement wall 59.
A rotary shaft 61 of the throttle lever 57 is inserted into a guide hole 62 of the case 52. The guide hole 62 guides the rotary shaft 61 such that the throttle lever 57 rotates about a contacting point of the engagement wall 59 and the regulating member 60 as a fulcrum. A turn spring 63 is provided to minimize the stroke of the throttle adjustment wire 53 and to press the grip portion of the throttle lever 57 away from the handle pipe 51. Further, a locking lever 64 is provided opposite to the throttle lever 57 to be engaged/disengaged with respect to the throttle lever 57 at the initial position. The locking lever 64 has an engagement hook 65 to be engaged/disengaged with respect to the drum holding portion 55, and is kept pressed to be normally engaged with the throttle lever 57.
It is assumed that the sub lever 58 is in the position as shown in FIG. 13 (where the sub lever 58 has been frictionally rotated counterclockwise to the maximum). In this state, when the engagement hook 65 of the locking lever 64 is disengaged from the drum holding portion 55 and the throttle lever 57 is strongly gripped, the throttle lever 57 can be maximally rotated until the engagement wall 59 contacts the regulating member 60. As a result, the throttle adjustment wire 53 is drawn out to the maximum, the throttle opening degree is increased to the maximum, and the rotation speed of the engine increases to the maximum. The throttle opening degree can be set to the medium or the minimum by frictionally rotating the sub lever 58 such that the engagement wall 59 contacts the regulating member 60 at a corresponding position.
In the above-mentioned throttle adjustment device, once the sub lever 58 has been frictionally rotated, the throttle opening degree (rotation speed of the engine) can be constantly maintained by simply strongly holding the throttle lever 57, without finely adjusting the holding force. Thus, it is superior in the operability and workability. Moreover, the throttle lever 57 can be locked at the initial position by the locking lever 64 as shown in FIG. 13. Thus, in the non-working time, the engine can be prevented from being unintentionally driven.
However, in the above-mentioned throttle adjustment device, once the throttle lever 57 is locked at the initial position by the locking lever 64 as shown in FIG. 13, the throttle lever 57 can not be moved from the initial position even if a shock, for example, due to the brush cutter falling down is applied thereto. If such shock is applied to the throttle lever 57 being locked, components for locking, such as the throttle lever 57, the drum 54, the drum holding portion 55 and the locking lever 64, may be broken or damaged.